2018 Freightliner Cascadia DD15 SPN 3251 FMI 0 - High DPF Pressure

Question

My 2018 Cascadia is driving me nuts. I'm getting constant active regens every 200 miles or so. The dash keeps throwing SPN 3251 FMI 0 which indicates the DPF pressure is too high. It starts to derate after an hour of highway driving. I've already replaced the outlet pressure sensor thinking it was just a bad reading, but the code came right back after 50 miles.

The truck has 450k miles on it and I don't see any black smoke, but the delta P readings are spiked even after a parked regen. I'm worried the DPF is completely plugged or maybe the 7th injector is leaking and loading the face of the brick. Does anyone know if this is usually a sensor issue or if I'm looking at a full DPF cleaning/replacement?

FuelInjFelix · Answer

✅ Confirmed fix: At 450k miles, your DPF is likely ash-loaded, not just soot-loaded. A parked regen only burns off soot, it doesn't remove ash. You need to pull the DPF and have it professionally cleaned or replaced. While it's out, inspect the face of the DOC for oil or coolant staining. In my case, it was a heavy ash load combined with a partially restricted venturi pipe causing false pressure spikes.

SCR_Sergei · Answer

Before you pull the filters, check your DOC inlet temps. If the DOC isn't getting hot enough, you won't get a good passive regen and it'll soot up fast. You might have a faulty HC doser (7th injector) that is leaking or has a weak spray pattern, causing face plugging on the DPF.

2018 Freightliner Cascadia DD15 SPN 3251 FMI 0 - High DPF Pressure

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